As we all know, C language has nasty (for compiler developers)
feature: setjmp/longjmp. If there is "setjmp" point in procedure, than
to explicitly express control flow we have to create control flow
edges from ALMOST EVERY reachable (from "setjmp" point) operation to
that "setjmp" point. This is TOO costly (both in memory requirements
and compilation time), so we decided not to make such edges. Of
course, this decision prohibit application of wide class of
optimizations in such procedures, but this is inevitable cost (AFAIK,
gcc compiler works exactly same way).

But we can't disable one special optimization: register
allocation. So, that's where the problem is: if r.a. based on
classical graph coloring approach, we must construct Register
Interference Graph (RIG), and hence we must take into account this
nasty feature of "setjmp" points. But how to do it? I have some ideas,
but they all are less than ideal, so any help will be gratefully
appreciated.